Case Studies

Taxonomic changes and bryogeography

Over time various species undergo changes in status. Whenever a group of bryophytes is studied in detail, with the benefits of the latest scientific tools, it's possible that what were once thought to be two different species are really variants of just one species. Conversely, what was thought to be one widely distributed species may turn out to be two distinct species. Such changes in status are especially likely when species that were defined long ago are re-studied. The OLD LITERATURE AND NEW IDEAS page gave a brief account of the issue.

Not surprisingly such changes in status (or taxonomic changes) can have an impact on bryogeographical hypotheses. The PROBLEMS AND PUZZLES page mentioned hornworts as a group with a high proportion of vaguely defined species. Until those problem species are cleared up it's impossible to get a good idea as to how many, and which, hornwort species are widespread and how many are confined to particular geographic regions. The liverworts and mosses also have their poorly understood groups. In the next three paragraphs we'll look at some specific examples to illustrate the possible range of effects of clearing up poorly defined or mis-understood species.

Telaranea claritexta is a leafy liverwort known from New South Wales and Western Australia. For many years the species had been known only from Western Australia and another species, Lepidozia whiteleggeana, from New South Wales. A description of the latter species had been published in 1909, based on specimens collected by Thomas Whitelegge (1850-1927) near the " Cook River, Botany Bay". The genera Telaranea and Lepidozia are closely related and in the past there has been much confusion about the species in these genera. A study published in 2004 concluded that Lepidozia whiteleggeana was identical to Telaranea claritexta, rather than being a separate species. There are rules as to what happens when two species are deemed identical but there's no need to go into detail here. By those rules the name Telaranea claritexta takes priority over Lepidozia whiteleggeana and is the name that remains in use. Technically, Lepidozia whiteleggeana has been synonymized with Telaranea claritexta. The addition of New South Wales to the geographic range of Telaranea claritexta was based solely on the re-examination of the original Whitelegge material, rather than on new collections from New South Wales, and the Whitelegge collection is still the only evidence for the occurrence of Telaranea claritexta in New South Wales. By contrast, the species has been found in a number of well-separated locations in south-west Western Australia. The equating of Lepidozia whiteleggeana with Telaranea claritexta raises one immediate question: Does the species occur anywhere between Botany Bay and Western Australia?

Frullania falciloba gives another synonymization example. This leafy liverwort, found in Australia and New Zealand, is one of the commonest Frullania species in southern Australia. A description of the species was first published in 1844, before Stephani's time. Between 1910 and 1924 Stephani published descriptions of the following species, all based on Australian collections: Frullania asperifolia, Frullania binominata, Frullania forsythiana, Frullania knightiana and Frullania wattsiana. Research in the 1970s showed these to be unwarranted as the specimens on which they were based were just forms of Frullania falciloba. Unlike the Telaranea claritexta case, the synonymization of the Stephani names with Frullania falciloba led to no additions to the geographic range of the species. While there need not be changes in geographical ranges when species are synonymized there will obviously always be a reduction in the number of species. In the Telaranea/Lepidozia example one species "disappeared", in the Frullania example it was five. Lepidozia whiteleggeana and Stephani's above five Frullania species were known only from the original collections, so all were notionally endemic. In effect, synonymization has removed six species from the endemic category – but those six should not have been counted as such anyway.

So far we've looked at hornworts and liverworts, so we'll finish this series of examples with the moss Ptychomitrium muelleri and a dramatic change in bryogeographic status after synonymization. A description of the species was first published in 1860 (under the name Glyphomitrium muelleri) and it was long thought to be essentially a moss of the eastern Australian mainland. Lord Howe Island was the only other place where it had been found. According to studies published in 1999 and 2001 Ptychomitrium balansae (found in South America), Ptychomitrium eurybasis (southern Africa) and Ptychomitrium neo-caledonicum ( New Caledonia) are synonyms of Ptychomitrium muelleri. The original descriptions of the three synonymous species had been published between 1877 and 1922. You can clearly see the marked change after synonymization, from four regional species to one that is widespread in the Gondwanan area.

There are still many bryophyte species that are poorly understood in Australia and which may undergo changes similar to some of those you've seen in the preceding paragraphs. Clearly you should treat any counts and distributions of Australian species (endemic or otherwise) with care and look at the foundations on which they're based. It's possible that future research will show some of the statements made in the ENDEMIC AUSTRALIAN BRYOPHYTES and the bryophytes of AUSTRALIA AND ELSEWHERE pages to be wrong. However, in an attempt to reduce that possibility, the examples have been chosen from species that have been defined or re-studied in fairly recent times by knowledgeable bryologists.

Change in genus

From time to time bryologists find that a species that has been placed in one genus really belongs in a different genus. There are various possible reasons and here are just two. The person who originally described the species may have missed some critical feature and so placed it in the wrong genus because of that oversight. Or someone, who finds that the species within a particular genus form a very mixed group, divides up the old genus to create a number of new genera, each of which contains more homogenous species.

If a species is transferred from genus A to genus B with no other change (for example, there's no synonymization of two or more species) there's no bryogeographic effect at the species level. In such cases the names change but endemic species remain endemic, bipolar species remain bipolar and so on. Of course, at the genus level, there may be a bryogeographic effect. Suppose again that a species is transferred from genus A to genus B, that all the species previously in genus A were found only in the Holantarctic Kingdom and that all the previously known species in genus B were known only from the Holarctic Kingdom. Those Kingdoms are defined near the beginning of the introductory BRYOGEOGRAPHY page. After the transfer there's no change in the bryogeographic status of any species, there's no change in the bryogeographic status of genus A but genus B has changed from a Holarctic to a bipolar genus.

The authors of a study published in 2002 defined the moss genus Arbusculohypopterygium. Previously the genus Dendrohypopterygium had contained two species: Dendrohypopterygium arbuscula (found in South America) and Dendrohypopterygium filiculiforme (found in New Zealand). The study reported that the molecular evidence was against keeping the two species in the same genus and that there were morphological features consistent with the molecular evidence. The authors therefore defined the new genus Arbusculohypopterygium, into which they transferred the species Dendrohypopterygium arbuscula. That was and has remained an endemic South American species. Dendrohypopterygium filiculiforme was and has remained an endemic New Zealand species. Dendrohypopterygium had been a genus with a New Zealand-South American distribution but is now confined to New Zealand.

A description of the moss species Calymperes latifolium was published in 1846, based on a specimen collected near Perth. While there is a close resemblance to the genus Calymperes a more careful examination of Calymperes latifolium showed that it didn't really fit in that genus, nor in any known genus. Therefore, in a paper published in 1985, the new genus Calymperastrum was defined to accommodate the species, so Calymperes latifolium became Calymperastrum latifolium. It is still the only species in the genus. The genus Calymperes is widespread through the tropical and sub-tropical areas of the world and contains many species, while Calymperastrum is known only from the south-west of Western Australia. The taxonomic change created what is, at least for now, an endemic genus for Australia. At the time of the publication of the 1985 paper the species Calymperastrum latifolium was known from one other location. A specimen had been collected in 1971 at Windy Harbour on the south-west corner of Western Australia. In 1994 another specimen was collected in the Windy Harbour region. All three of the Calymperastrum specimens referred to above were found growing on Macrozamia. Coincidence or does the species have a preference for Macrozamia? Until more specimens are found that will have to remain an open question.